The proposed research involves the use of primary neonatal mouse and adult human keratinocytes in culture to define the modulation by additives of epidermal cell function. Function is defined in the cultures as proliferation as assayed by 3H-Tdr incorporation into isolated DNA and autoradiographic determination of the labeling index, and specialization or differentiation defined as the production and final assembly of structural proteins (keratins, keratohyalin, filaments, cornified cell envelopes) by the keratinocytes. Specialization is quantitatively and qualitatively measured by 3H histidine pulse chase labeling of the cultures and determination of 3H uptake into sequentially extracted fractions: the high molarity salt extractable proteins (soluble keratohyalin and keratohyalin macroaggregates); SDS soluble proteins (pre-keratin and other proteins); 4 M urea soluble proteins (keratins); and 8 M urea plus reducing agents soluble and insoluble fractions (disulfide cross-linked keratins). SDS polyacrylamide gel electrophoresis (SDS-PAGE) is used to further isolate and classify the labeled proteins. By use of these techniques and the neonatal mouse and adult human keratinocyte primary cultures, we propose to study the patterns of 3H-histidine labeling in vitro as the cultures develop over time, and in response to a spectrum of additives, i.e., glucocorticoids, cyclic nucleotides, retinoyl acetate, epidermal hyperplastic agents, arachidonic acid and its biologically active products, EFG. The proliferative response of the cells to the additives will be determined. The effects of combined epidermal cell modulators will be determined, as well as the interaction of selected agents with keratinocytes grown under fibroblastic influence will be studied. The results of the proposed investigations can yield information contributing to an understanding of epidermal homeostatic control systems and can result in improved therapies for the treatment of cell proliferation-specialization disorders in general, and specifically, of the human skin disease psoriasis.